Melatonin is nicknamed the Dracula hormone because it is usually secreted at night and this secretion is suppressed by ocular light exposure. In term pregnancies, labor is more often initiated at night. There are melatonin receptors on the pregnant uterus that are activated at term during labor. We propose to use these three physiological facts as the basis for testing a potential non-invasive intervention for altering uterine contractions in late-term pregnant women: photic suppression of endogenous melatonin secretion. The mammalian eye processes light exposure through visual and non-visual cells and pathways. Physiological functions affected by non-visual light exposure include hormone concentrations (e.g., melatonin suppression), circadian rhythm phase and amplitude, subjective alertness, and the pupillary light reflex. The melatonin response to light is how seasonally-reproductive animals monitor daylength. Light-induced suppression of melatonin and other physiological functions is wavelength dependent; these non-visual light responses are most sensitive to blue/green wavelengths and much less to red wavelengths. In our recent studies in six late-term pregnant women that included nighttime ocular light exposure, women who were exposed to blue/green light had lower concentrations of melatonin and fewer uterine contractions than those exposed to red light. There was a significant positive relationship (R2 = 0.87) between the total amount of melatonin secreted and the total number of contractions during the light exposure. These exciting preliminary data make this research proposal ideal for the NIH R21 mechanism in that (i) it is a new exploratory and developmental research project; (ii) currently available data on this topic are limited; and (iii) these studies may lead to a breakthrough in better understanding of physiology and development of novel techniques, methodologies, and applications that could have a major impact on a field of biomedical and clinical research and practice. We have demonstrated our ability to conduct all aspects of the study, including recruitment, outpatient and inpatient monitoring, experimental light exposure and physiological data collection of melatonin concentrations and uterine contractions. Ramifications of these findings for the practice of obstetrics could be dramatic. If ocular light exposure were able to suppress pre-term labor (which occurs in more than 12% of all pregnancies), it would be an inexpensive, non-obtrusive, easy- to-use method with minimal side effects. Of equal importance, the use of pharmaceutical melatonin in addition to oxytocin might be beneficial in inducing labor, including allowing reduction of the concentrations of oxytocin administered.